Method and system for removing ash within a particulate filter

ABSTRACT

Methods and systems are provided for injecting water to reduce an ash load on a PF. In one example, a method may include injecting water from a reservoir to between a PF and a three-way catalyst in order to reduce an ash load.

FIELD

The present description relates generally to methods and systems forremoving ash within an emission control device.

BACKGROUND/SUMMARY

The exhaust gas emitted from an internal combustion engine may include aheterogeneous mixture that may contain gaseous emissions such as carbonmonoxide (CO), unburned hydrocarbons (HC), nitrogen oxides (NO_(x)), andcondensed phase materials (liquids and solids) that constituteparticulate matter (PM). Transition and primary group metal catalyststypically coat a catalyst support along with substrates to provide anengine exhaust system the ability to convert some, if not all of theseexhaust components into other compounds.

Exhaust aftertreament systems may include a three-way catalyst (TWC) anda particulate filter (PF). The TWC provides a passage for gaseousemissions to flow through and undergo oxidation and reduction reactionwith the catalytic components. The TWC may not comprise a bindingelement, whereas the PF may comprise a binding element to capture PM.

Over time, the PF may become full and a regeneration operation may beused to remove trapped particulates. The regeneration involvesincreasing the temperature of the particulate filter to a relativelyhigh temperature, such as above 600° C., in order to burn theaccumulated particulates into ash.

A potential drawback with the regeneration process is ash accumulationsubsequent to the regeneration process in spark-ignited engines. Thehigh-exhaust temperatures of spark-ignited engines (e.g., 550° C.)vaporize the water released after combustion, thereby disabling theability for water to sweep the ash from the exhaust pathway. This isgenerally in contrast to diesel engines where the water is not vaporizeddue to lower exhaust temperatures (e.g., 90° C.) and is able to reducethe ash load. One example attempt to address ash build up includesinjecting air to reduce ash accumulation, such as described in Sorensenet al. in U.S. Patent No. 2011/0120090. Therein, an oxygen injection isused to further burn an ash accumulation and remove it from the PF.

However, the inventors herein have also recognized potential issues withsuch systems. As one example, an oxygen injection upstream of a PF mayincrease an exhaust gas temperature above a threshold that may degradethe filter. By injecting air to initiate a regeneration, theregeneration temperature may be more difficult to regulate and increasea PF temperature to a temperature in which the PF may be degraded.

In one example, the issues described above may be addressed by a methodfor injecting water from a reservoir to between a catalyst brick and aparticulate filter. In this way, the water injection carries the ashtoward the back and out of the PF and simultaneously maintains anexhaust gas temperature within a range that does not degrade the PF.Further, the water injection can increase the PF capacity to captureemission particles.

The above discussion includes recognitions made by the inventors and notadmitted to be generally known. Thus, it should be understood that thesummary above is provided to introduce in simplified form a selection ofconcepts that are further described in the detailed description. It isnot meant to identify key or essential features of the claimed subjectmatter, the scope of which is defined uniquely by the claims that followthe detailed description. Furthermore, the claimed subject matter is notlimited to implementations that solve any disadvantages noted above orin any part of this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic diagram of an engine with a three-way catalyst(TWC) upstream of a particulate filter (PF).

FIG. 2 shows a flow chart illustrating an exemplary method forregenerating a particulate filter and performing direct injectionbetween the TWC and the PF.

FIG. 3 shows a flow chart demonstrating an exemplary method for directinjecting a fluid at a space between the TWC and the PF.

FIG. 4 shows a graph illustrating a variety of engine conditions forinitiating a water injection.

DETAILED DESCRIPTION

The following description relates to a method for injecting water toreduce an ash load on a particulate filter (PF) surface nearest to alocation between the PF downstream of a three-way catalyst (TWC). The PFand TWC may be located in an engine exhaust emission control device. Theengine exhaust emission control device may include an injector port anda pressure sensor. Further, the water injection may be used to maintaina PF temperature.

A PF may capture and store soot. The soot load may decrease exhaust flowthrough the PF and as the soot load increases, the exhaust flow throughthe PF may by impeded enough to create an undesired amount ofbackpressure that can decrease engine efficiency. In order to reducesuch backpressure, a PF regeneration may occur responsive to an exhaustgas pressure being greater than a threshold exhaust gas pressure. As thePF undergoes a regeneration, a portion of the soot is converted into agas and a separate portion is converted into ash. The ash may accumulateonto the PF nearest a space between the TWC and the PF. After a numberof PF regenerations (e.g., 100), the ash load may cause increasedexhaust backpressure and/or reduce soot trapping and regenerationeffectiveness. However, because the exhaust backpressure increase may becaused by either the high soot load prior to regeneration or the highash load following the regeneration, the present application providesfor, in one example, a method carried out by a controller of a controlsystem for differentiating the two causes of increased backpressurealong with a method for injecting water into a space between the PF andthe TWC based on the differentiation.

FIG. 1 is a schematic diagram showing one cylinder of multi-cylinderengine 10, which may be included in a propulsion system of anautomobile. Engine 10 may be controlled at least partially by a controlsystem including controller 12 and by input from a vehicle operator 132via an input device 130. In this example, input device 130 includes anaccelerator pedal and a pedal position sensor 134 for generating aproportional pedal position signal PP. Combustion chamber (i.e.,cylinder) 30 of engine 10 may include combustion chamber walls 32 withpiston 36 positioned therein. In some embodiments, the face of piston 36inside cylinder 30 may have a bowl. Piston 36 may be coupled tocrankshaft 40 so that reciprocating motion of the piston is translatedinto rotational motion of the crankshaft. Crankshaft 40 may be coupledto at least one drive wheel of a vehicle via an intermediatetransmission system. Further, a starter motor may be coupled tocrankshaft 40 via a flywheel to enable a starting operation of engine10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust passage48. Intake manifold 44 and exhaust passage 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves.

Intake valve 52 may be controlled by controller 12 via electric valveactuator (EVA) 51. Similarly, exhaust valve 54 may be controlled bycontroller 12 via EVA 53. Alternatively, the variable valve actuator maybe electro hydraulic or any other conceivable mechanism to enable valveactuation. During some conditions, controller 12 may vary the signalsprovided to actuators 51 and 53 to control the opening and closing ofthe respective intake and exhaust valves. The position of intake valve52 and exhaust valve 54 may be determined by valve position sensors 55and 57, respectively. In alternative embodiments, one or more of theintake and exhaust valves may be actuated by one or more cams, and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems to vary valve operation. For example, cylinder 30 mayalternatively include an intake valve controlled via electric valveactuation and an exhaust valve controlled via cam actuation includingCPS and/or VCT.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to a spark advance signal SA fromcontroller 12, under select operating modes.

Intake passage 42 may include throttles 62 and 63 having throttle plates64 and 65, respectively. In this particular example, the positions ofthrottle plates 64 and 65 may be varied by controller 12 via signalsprovided to an electric motor or actuator included with throttles 62 and63, a configuration that is commonly referred to as electronic throttlecontrol (ETC). In this manner, throttles 62 and 63 may be operated tovary the intake air provided to combustion chamber 30 among other enginecylinders. The positions of throttle plates 64 and 65 may be provided tocontroller 12 by throttle position signals TP. Intake passage 42 mayinclude a mass air flow sensor 120 and a manifold air pressure sensor122 for providing respective signals MAF and MAP to controller 12.

Further, in the disclosed embodiments, an exhaust gas recirculation(EGR) system may route a desired portion of exhaust gas from exhaustpassage 48 to intake passage 44 via high pressure EGR (HP-EGR) passage140 or low pressure EGR (LP-EGR) passage 150. The amount of EGR providedto intake passage 44 may be varied by controller 12 via HP-EGR valve 142or LP-EGR valve 152. Further, an EGR sensor 144 may be arranged withinthe HP-EGR passage and may provide an indication of one or more ofpressure, temperature, and concentration of the exhaust gas.Alternatively, the EGR may be controlled through a calculated valuebased on signals from the MAF sensor (upstream), MAP (intake manifold),MAT (manifold gas temperature) and the crank speed sensor. Further, theEGR may be controlled based on an exhaust O₂ sensor and/or an intakeoxygen sensor (intake manifold). Under some conditions, the EGR systemmay be used to regulate the temperature of the air and fuel mixturewithin the combustion chamber. FIG. 1 shows a high pressure EGR systemwhere EGR is routed from upstream of a turbine of a turbocharger todownstream of a compressor of a turbocharger and a low pressure EGRsystem where EGR is routed from downstream of a turbine of aturbocharger to upstream of a compressor of the turbocharger. In someembodiments, engine 10 may include only an HP-EGR system or only anLP-EGR system. In further embodiments, engine 10 may not include aturbocharger.

As such, engine 10 may further include a compression device such as aturbocharger or supercharger including at least a compressor 162arranged along intake manifold 44. For a turbocharger, compressor 162may be at least partially driven by a turbine 164 (e.g., via a shaft)arranged along exhaust passage 48. For a supercharger, compressor 162may be at least partially driven by the engine and/or an electricmachine, and may not include a turbine. Thus, the amount of compressionprovided to one or more cylinders of the engine via a turbocharger orsupercharger may be varied by controller 12. Further, turbine 164 mayinclude wastegate 166 to regulate the boost pressure of theturbocharger. Similarly, intake manifold 44 may include valved bypass167 to route air around compressor 162.

Emission control devices 71 and 72 are shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Devices 71 and 72 maybe a selective catalytic reduction (SCR) system, three way catalyst(TWC), NO_(x) trap, various other emission control devices, orcombinations thereof. In the example illustrated in FIG. 1, device 71 isa TWC and device 72 is a particulate filter (PF). In some embodiments,the TWC 71 and the PF 72 may be housed in a common housing of anemission control device 74 (as shown in FIG. 1) and separated via an airgap. In alternative embodiments, emission control system housing 74 maybe dispensed with and the TWC and PF each housed in separate housingsand fluidically coupled via the exhaust passage (not shown in FIG. 1).Further, in some embodiments, during operation of engine 10, emissioncontrol devices 71 and 72 may be periodically reset by operating atleast one cylinder of the engine within a particular air/fuel ratio.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 74. Further, sensor 127 is shown coupled toexhaust passage 48 between a particulate filter 72 and a three-waycatalyst 71 via a boss 76 located in exhaust control device 74. Sensor128 is shown coupled to exhaust passage 48 downstream of particulatefilter 72. Sensors 127 and 128 may measure an exhaust pressure upstreamand downstream of the particulate filter 72 to determine a pressure dropacross the particulate filter (also referred to as the exhaust deltapressure). If the exhaust delta pressure is greater than a thresholdexhaust delta pressure, it may indicate that particulate matter (e.g.,soot) and/or ash have accumulated on the particulate filter to a highenough degree to impede desired exhaust flow through the particulatefilter. In response to the large pressure drop across the particulatefilter, a particulate filter regeneration to burn off particulate matterand/or a water injection to remove built up ash may be performed, asdescribed in more detail below. In alternative embodiments, sensor 128may not be included and sensor 127 may be an absolute or gauge pressuresensor.

The three-way catalyst comprises a porous substrate coated with one ormore precious metals. The three-way catalyst is configured to convertone or more emissions in exhaust gas flowing through the three-waycatalyst. The particulate filter comprises a mesh structure. In someexamples, the particulate filter may comprise one or more preciousmetals, wherein a precious metal mass of the particulate filter is lessthan a precious metal mass of the three-way catalyst. As an example, ifthe three-way catalyst comprises 100 g of precious metals, then theparticulate filter may comprise 25 g of precious metals. In someexamples, a four-way catalyst may be used in place of the three-waycatalyst, the four-way catalyst may include the particulate filterintegrated with the three way catalyst. The particulate filter isconfigured to trap soot in exhaust gas flowing through the particulatefilter.

Reservoir 70 may store water in one example. In other examples,reservoir 70 may store another suitable fluid or a fluid mixture (e.g.,water and methanol/ethanol/glycol) in order to reduce the freezing pointof the water. Conduit 75 and water injector 73 fluidically couple thereservoir 70 to an air gap between the TWC 71 and the PF 72. The boss 76accommodating pressure sensor 127 may also accommodate water injector73, wherein the injector is positioned to inject water between the TWCand the PF. In alternative embodiments, separate bosses may be used tohouse the water injector 73 and the pressure sensor 127. The waterinjector may be controlled via signals sent from a controller (e.g.,controller 12). Water injection into the air gap between the TWC 71 andthe PF 72 may be responsive to a pressure sensor measurement beinggreater than a threshold pressure (e.g., pressure sensor 127 measures anexhaust gas pressure greater than a threshold exhaust gas pressure). Thewater injection may further be responsive to a PF regenerationtemperature being greater than a threshold regeneration temperature.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Controller 12 may receive varioussignals from sensors coupled to engine 10, in addition to those signalspreviously discussed, including measurement of inducted mass air flow(MAF) from mass air flow sensor 120; engine coolant temperature (ECT)from temperature sensor 112 coupled to cooling sleeve 114; a profileignition pickup signal (PIP) from Hall effect sensor 118 (or other type)coupled to crankshaft 40; throttle position (TP) from a throttleposition sensor; and absolute manifold pressure signal, MAP, from sensor122. Engine speed signal, RPM, may be generated by controller 12 fromsignal PIP. Manifold pressure signal MAP from a manifold pressure sensormay be used to provide an indication of vacuum, or pressure, in theintake manifold. Note that various combinations of the above sensors maybe used, such as a MAF sensor without a MAP sensor, or vice versa.During stoichiometric operation, the MAP sensor can give an indicationof engine torque. Further, this sensor, along with the detected enginespeed, can provide an estimate of charge (including air) inducted intothe cylinder. In one example, sensor 118, which is also used as anengine speed sensor, may produce a predetermined number of equallyspaced pulses every revolution of the crankshaft.

Storage medium read-only memory 106 can be programmed with computerreadable data representing instructions executable by processor 102 forperforming the methods described below as well as other variants thatare anticipated but not specifically listed.

As described above, FIG. 1 shows only one cylinder of a multi-cylinderengine, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

As described previously, injector 73 provides water to between the TWC71 and the PF 72. This method may be used to reduce an ash load on thesurface of the PF nearest the TWC. Functions of the system aredetermined by controller 12 and are further explained in FIG. 2.

FIG. 2 is a flow chart illustrating an exemplary method for regeneratinga particulate filter and injecting water between the TWC and the PF thatmay be carried by a control system including the controller andprocessor in combination with one or more sensors, one or moreactuators, and/or one or more other hardware components such as thedescribed engine exhaust system. Portions of the actions described inthe routine of FIG. 2 may be structurally formed as instructions storedin non-transitory memory.

Continuing with FIG. 2, the water injection may either decrease an ashload on the PF surface nearest the space between the TWC and the PF ordecrease a PF temperature in order to prevent PF degradation. Forexample, the ash may accumulate on the PF in a region that is closer tothe TWC, or more upstream, in some examples. As described above, theinjection between the TWC and the PF may include water. In someexamples, the injection may also be accomplished with a fluid mixture(e.g., water and methanol/ethanol/glycol). The mixture may be injectedduring instances where water would otherwise be frozen (e.g., enginecold start) as determined by the controller.

Method 200 will be described herein with reference to components andsystems depicted in FIG. 1, particularly, regarding TWC 71, PF 72, waterreservoir 70, water injector 73, pressure sensors 127 and 128, emissioncontrol device 74, turbine 164, wastegate 166, and exhaust pathway 48.Method 200 may be carried out by a controller (e.g., controller 12)according to computer-readable media stored thereon. In some examples,method 200 may be performed in a spark-ignition engine, and as suchduring execution of the method, fuel in the engine may be combusted viaspark ignition and exhaust gas from the engine may be directed to theparticulate filter. It should be understood that the method 200 may beapplied to other systems of a different configuration without departingfrom the scope of this disclosure.

Method 200 may begin at 202, wherein engine operating conditions may beestimated and/or measured. The engine operating conditions may include,but are not limited to an exhaust gas temperature, an engine load andspeed, an exhaust gas pressure, and a commanded air/fuel ratio. At 204,the method includes measuring the exhaust gas pressure between the TWCand the PF. In one example, there are no other components between apressure sensor and the TWC in the upstream direction, and the pressuresensor and the PF in the downstream direction, other than injector 75.In other examples, additional components may be added, if desired. Insome examples where the TWC and PF are housed in a common housing, theexhaust gas pressure may be measured at an air gap within the housingbetween the TWC and PF. In other examples where the TWC and PF arehoused in separate housings coupled via an exhaust passage, the exhaustgas pressure may be measured at the exhaust passage between the TWC andPF. The exhaust gas pressure may be measured by a gauge pressure sensoror an absolute pressure sensor. For example, pressure sensor 127,accommodated via boss in the housing between the TWC and the PF, maymeasure an exhaust gas pressure in the air gap, as explained above withrespect to FIG. 1. As another example, emission control device 74 mayhouse delta pressure sensors 127 and 128, wherein pressure sensor 127measures an exhaust gas pressure in an air gap and pressure sensor 128measures an exhaust gas pressure downstream of the PF, as explainedabove with respect to FIG. 1.

At 206, the method includes comparing the exhaust gas pressure betweenthe TWC and the PF to a first threshold exhaust pressure. The firstthreshold exhaust pressure may be a suitable pressure that indicates arelatively high level of soot and/or ash has accumulated on the PF. Forexample, a soot load greater than the threshold soot load may impedeexhaust flow through the PF. In one example, if the exhaust gas pressureis measured by a gauge/absolute pressure sensor, then the firstthreshold exhaust pressure may be a first threshold gauge/absoluteexhaust pressure. In another example, if the delta exhaust pressure ismeasured by upstream and downstream pressure sensors, then the firstthreshold exhaust pressure may be a first threshold delta exhaustpressure. If the exhaust pressure is greater than the first thresholdexhaust pressure, then the method proceeds to 210, which will beexplained in more detail below. Briefly, as explained above, the exhaustpressure may be greater than the first threshold exhaust pressure due toa soot load and/or an ash load being greater than a threshold, and as aresult a PF regeneration may be carried out to burn off the accumulatedsoot. This PF regeneration demand may be based on a soot load on the PFexceeding a threshold soot load. On the other hand, if the exhaustpressure is less than the first threshold exhaust pressure, then themethod proceeds to 208. At 208, the method includes maintaining currentengine operating parameters and not conducting a PF regeneration. Themethod may exit.

At 210, the method includes determining if regeneration conditions aremet. The PF regeneration may be either passive or active. If theregeneration is passive, the regeneration conditions may include avehicle speed exceeding a threshold vehicle speed (e.g., 40 mph) and/oran engine load exceeding a threshold engine load. If the passiveregeneration conditions are not met, then the method proceeds to 208. At208, the method includes maintaining current engine operatingparameters, as described above. The method may return to continue tomonitor for conditions suitable for performing the regeneration.

If the regeneration is active, engine operating parameters may bepurposely adjusted to increase exhaust gas temperature to a temperaturehigh enough to initiate combustion of the stored soot on the PF. Theengine operating parameters that may be varied may include one or moreof increasing an oxygen content in the intake air and/or exhaust (e.g.,by adjusting a throttle position), retarding spark, and delaying fuelinjection timing. In some examples, the regeneration may be carried outonly if the current operating parameters allow for the changes listedabove and/or if such changes will actually result in a high enoughexhaust temperature to perform the regeneration. For example, theregeneration may not be performed during a cold engine start. If theactive regeneration parameters are not met, then the method proceeds to208. Further, the regeneration may occur during a subsequent iterationof the method 200 when the active regeneration conditions are met. Inalternative embodiments, a controller (e.g., controller 12) may signalfor the active regeneration adjustments to occur regardless of currentengine operating parameters. At 208, the method includes maintainingcurrent engine operating parameters, as described above. The method mayexit.

If either the passive or active regeneration conditions are met, themethod proceeds to 212, wherein the regeneration is performed. Duringthe regeneration, the air/fuel ratio may be leaned, spark may beretarded, and/or the fuel injection may be delayed in order to increasean exhaust gas temperature. The hotter, lean exhaust gas may allow thePF to combust and self-burn the stored soot. As a result, if the exhaustgas oxygen content and temperature increase, then the faster the PFself-burns and regenerates the soot. For a given exhaust gas temperatureunder regeneration conditions, a total duration of regeneration may bebased on a total soot load stored on the PF. The total soot load on thePF may be estimated based on a difference between the exhaust gaspressure and the first threshold exhaust pressure, for example, or basedon engine operating parameters since a previous PF regeneration hasoccurred. The exhaust gas pressure greater than the first thresholdexhaust pressure indicates a PF regeneration demand and that the sootload on the PF is greater than a threshold soot load. Therefore, as thedifference between the exhaust gas pressure and the first thresholdexhaust pressure increases, the estimated soot load on the PF increases(e.g., the increasing soot load further impedes the flow of exhaust gasthrough the PF and increases exhaust backpressure). As a result, as theestimated soot load increases and/or the exhaust gas temperaturedecreases, the total duration of regeneration increases. Further, as theestimated soot load decreases and/or the exhaust gas temperatureincreases, the total duration of regeneration decreases.

However, the regeneration may be halted due to a change in engineoperating parameters. As an example for a passive regeneration, theregeneration may be halted and/or interrupted due to an engine loadbeing less than a threshold load. As the engine load decreases, theair/fuel ratio becomes richer and as a result, the PF self-burn does notreceive an amount of oxygen sufficient to keep the self-burn active.Therefore, instances may occur where the PF regeneration is anincomplete PF regeneration (e.g., the regeneration is interrupted).

At 214, the method includes determining if the PF regeneration iscomplete. A complete PF regeneration may be based on running aregeneration for a predetermined period of time (e.g., 10 minutes),reaching a PF regeneration temperature (e.g., 800° C.), reducing a sootload to a relatively low load, or a combination of all three. If it isdetermined that a regeneration is incomplete, then the method proceedsto 216. At 216, the method includes determining if the regeneration wasinterrupted based on conditions described above (e.g., an engine loaddropping below a threshold engine load). If the regeneration was notinterrupted, then the method proceeds to 212 and continues to performthe regeneration.

However, if the regeneration is complete or if the regeneration wasinterrupted, then the method proceeds to 218. At 218, the methodincludes measuring an exhaust pressure between the TWC and the PF (e.g.,at the air gap), similar to the process described above with respect to204 in order to estimate an ash load on the PF surface nearest the spacebetween the TWC and the PF. As explained previously, as exhaust flowsthrough the emission control device (e.g., emission control device 74),soot is stored on a PF (e.g., PF 72). The soot may block the flow ofexhaust gas through the PF, and create exhaust backpressure (e.g.,increased exhaust pressure upstream of the PF). In response to theincreased backpressure, signaled by an exhaust pressure being greaterthan a first threshold exhaust pressure, the controller (e.g.,controller 12) may signal for a regeneration. As the regeneration isperformed, the soot is burned into ash, which may accumulate on theupstream PF surface. As the ash accumulates over a number of PFregenerations (e.g., 100), the ash load may increase enough to causeexhaust backpressure. Therefore, the exhaust pressure measurement may beused to detect either a regeneration demand or a water injection demanddepending on when the exhaust pressure signal is queried. As a result,the exhaust pressure may be measured prior to a regeneration event aswell as immediately following the PF regeneration in order to determineif the backpressure is a result of the soot load being greater than thethreshold soot load or the ash load being greater than the threshold ashload. As used herein, the term “immediately” may include a suitableduration of time after regeneration has been determined to havecompleted or interrupted but before soot begins to rebuild on the PF,such as within 5 minutes or less of a PF regeneration.

At 220, the measured exhaust pressure is compared to a second thresholdexhaust pressure. In one embodiment, the second threshold exhaustpressure may be equal to the first threshold exhaust pressure. In asecond embodiment, the second threshold exhaust pressure may be based onan expected exhaust gas pressure. The expected exhaust gas pressure maybe based on the previous PF regeneration. For example, if the PFregeneration was interrupted, then the expected exhaust pressure may behigher than an expected exhaust pressure for a completed PFregeneration. Further, the expected exhaust pressure may be based on aPF regeneration temperature and/or a PF regeneration duration. In otherwords, as the PF regeneration duration and/or temperature increases, theexpected exhaust gas pressure decreases. If the exhaust pressure is lessthan the second threshold exhaust pressure, then the ash load is notgreater than a threshold ash load and no water injection occurs. Themethod proceeds to 208 and maintains current engine operatingparameters, as described above. The method may exit.

If the exhaust pressure measurement following the PF regeneration isgreater than the second threshold exhaust pressure, then the ash loadmay be greater than the threshold ash load and be causing the pressurebackflow. The method proceeds to 222.

An ash load greater than the threshold ash load causes the exhaust gaspressure to be greater than the second threshold exhaust pressure byimpeding exhaust flow through the PF, and thus the ash load exceedingthe threshold ash load may be determined by the controller based on theexhaust pressure measurement occurring only at the selected timing asdescribed above. In other examples, the ash load may be predicted to begreater than the threshold ash load after a predetermined number of PFregenerations (e.g., 100). Further, in some examples the ash load may beestimated to exceed the threshold based on an estimated ash loadproduction. The estimated ash load production may be based on anestimated PF soot load prior to regeneration and the PF regenerationtemperature and the PF regeneration duration. The estimated ash loadproduction increases as the estimated soot load burned increases. Thepredicted ash load may increase as one or more of the estimated sootload increases, the PF regeneration temperature increases, and/or the PFregeneration duration increases.

As an example, a vehicle may begin a PF regeneration in response to ahigh soot load on a PF (e.g., 0.5 kg). The vehicle may adjust operatingparameters in order to increase exhaust gas temperature to a PFregeneration temperature (e.g., 650° C.). However the PF regenerationmay be interrupted and thus the regeneration may be incomplete. Thevehicle may be able to estimate an amount of soot burned based on theregeneration temperature and duration. Considering the regeneration isnot complete (e.g., 0.2 kg soot remains on the PF) and all burned sootis not converted into ash (e.g., 0.5 kg of burned soot converts to 0.05kg ash), a conversion factor may be used to estimate a newly formed ashload based on the regeneration conditions (e.g., 0.3 kg of soot may beburned resulting in 0.03 kg of ash). The ash loads may be added up overtime (e.g., after each regeneration event) to allow the controller topredict when the next water injection to reduce an ash load may occur.

At 222, the method includes determining if water injection conditionsare met. The water injection conditions may include determining if wateris available based on a temperature measurement or volume measurement ina water reservoir (e.g., reservoir 70). The temperature measurement maybe used to determine if the water is liquid phase water or frozen water(e.g., ice). The volume measurement may be conducted by an appropriategauge volume sensor and may be used to determine if enough water ispresent for the injection. Further, the water injection conditions mayfurther include measuring an exhaust gas temperature. As an example, itmay be preferred to inject water during conditions where the exhaust gastemperature is less than a threshold exhaust gas temperature (e.g., 100°C.). An injection where the exhaust gas temperature is less than thethreshold exhaust gas temperature allows the water to remain in theliquid phase and wash the ash from the surface of the PF nearest the TWCto the end of the PF. If the exhaust gas temperature is greater than thethreshold exhaust gas temperature, then the water may vaporize uponinjection and become unable to reduce the ash load. If water injectionconditions are not met, then the method proceeds to 224. At 224, themethod includes continuing to monitor the injection parameters until thewater injection conditions are met.

If injection conditions are met, the method proceeds to 226 and injectswater. As an example, a water injection duration and/or volume may beadjusted based on an estimated ash load described above, wherein as theestimated ash load increases, the water injection duration and/or volumemay also increase. As another example, a water injection duration and/orvolume may be based on a specific duration of injection regardless ofthe estimated ash load (e.g., 30 seconds). In one example, the waterinjection may be based on a predetermined value, regardless of theestimated ash load, wherein the water injection reduces the ash load toa relatively low amount an attenuates the exhaust backpressure. Inanother example, the water injection may be performed at a predeterminedwater injection rate such as 5 kg/hr. The water injection may wash theash that has accumulated on the upstream surface of the PF to the backof the PF and eventually to atmosphere. The method proceeds to 228.

At 228, the method includes optionally adjusting current engineoperating parameters to increase mass flow of exhaust through the PF toassist in the removal of the ash. In one embodiment, where the TWC isdownstream of a LP-EGR system, the adjusting may include opening awastegate and/or partially or fully closing an EGR valve in order toflow higher pressure and/or more exhaust through the TWC and the PF.However, this may only be performed when an engine dilution demand ismet in order to maintain desired exhaust emission levels, for example.By decreasing the EGR flow rate the likelihood of removing the ash fromthe back of the PF may be increased. The method may then exit.

FIG. 2 described an exemplary method of regenerating a PF and injectingwater between a TWC and a PF to decrease an ash load on the PF surfacenearest the space between the TWC and the PF. FIG. 3 will now describe amethod to inject water in order to maintain a PF temperature and/orreduce an ash load on the PF surface nearest the space between a TWC anda PF. The routine of FIG. 3 may be performed in combination with theroutine of FIG. 2, in one example.

FIG. 3 is a flow chart illustrating an example method 300 for injectingwater between a particulate filter (PF) and a three-way catalyst (TWC),wherein the PF is downstream of the TWC.

Method 300 will be described herein with reference to components andsystems depicted in FIG. 1, particularly, regarding TWC 71, PF 72, waterreservoir 70, water injector 73, pressure sensors 127 and 128, andemission control device 74. Method 300 may be carried out by acontroller (e.g., controller 12) according to computer-readable mediastored thereon. It should be understood that the method 300 may beapplied to other systems of a different configuration without departingfrom the scope of this disclosure.

Method 300 may begin at 302, wherein engine operating conditions may beestimated and/or measured. The engine operating conditions may include,but are not limited to an exhaust gas temperature, an engine load and/orspeed, an exhaust pressure, and a commanded air/fuel ratio. At 304, themethod 300 includes estimating if a PF temperature exceeds a thresholdPF temperature. A PF temperature greater than the threshold PFtemperature (e.g., a temperature above 1000° C.) may cause irreversibledegradation to the PF. The PF temperature may be directly measured by atemperature sensor in one example, or it may be inferred from operatingconditions, such as exhaust temperature, air-fuel ratio, soot load onthe PF, etc. The threshold PF temperature may be higher than thetemperature the PF typically reaches during a regeneration event. If thePF temperature is greater than the threshold PF temperature, then themethod proceeds to 310, which will be described below. However, if thePF temperature is less than the threshold PF temperature, then themethod proceeds to 306.

At 306, the method includes comparing an ash load on the PF surfacenearest the space between the TWC and the PF to a threshold ash load.The ash load may be estimated based on an estimated ash load production,as described above. Determining the ash load includes measuring anexhaust pressure in the air gap via a pressure sensor and comparing themeasured exhaust pressure to a second threshold exhaust gas pressure. Asdescribed above, the pressure sensor may be a gauge, an absolute, or adelta pressure sensor. If the measured exhaust pressure is greater thanthe second threshold exhaust gas pressure, then the ash load may begreater than the threshold ash load.

In an alternative embodiment, determining the ash load being greaterthan the threshold ash load may be based on a number of miles driven(e.g., 1000 miles) or driving over a threshold speed for a period oftime (e.g., 40 mph over 100 hours).

If the ash load is greater than the threshold ash load, then the methodproceeds to 310. If the ash load is less than the threshold ash load,then the method proceeds to 308. At 308, the method includes maintainingcurrent engine operating parameters and the fluid injection does notoccur. The method may exit.

At 310, the method includes determining if injection conditions are met.The injection conditions may include a water availability (e.g., enoughwater present in reservoir or water is liquid), as described above. If areservoir is does not have a sufficient volume of water for injection,the reservoir may be replenished via an external service port. Inalternative embodiments, the reservoir may be replenished via acondensate formed in a charge air cooler. The charge air cooler may befluidically coupled to the water reservoir, wherein the condensate fromthe charge air cooler flows to the water reservoir responsive to a fluidvolume gauge in the reservoir. Further, in some embodiments, an airconditioner drip tube may be fluidically coupled to the water reservoir,wherein the condensate from the air conditioner flow to the waterreservoir responsive to the fluid volume gauge in the reservoir. Themethod proceeds to 314 if water injection conditions are met. However,the method proceeds to 312 if the conditions are not met and thecontroller maintains current engine operating parameters as describedabove with respect to 308.

At 314, the method includes injecting water into a space (e.g., air gapor exhaust passage) between the TWC and the PF. The injecting isresponsive to a pressure signal being above a threshold pressure, asdescribed above. Further, the injecting may be responsive to aparticulate filter temperature being above a threshold temperature. Thewater injection impinges on the front surface of the PF and washes theash to the back of the PF. The exhaust gas then blows the ash out the PFand through the tailpipe and into the atmosphere.

Serendipitously, the water injection maximizes the PF capacity tocapture more soot. This may be due to the water providing the PF with anincreased adhesive surface area. Further, the water may provide improvedcapturing of NO_(x) and CO due to its polarity and ability to hydrogenbond to the gases. The amount of water injected may be determined basedon the estimated ash load, as described above. The method proceeds to316.

At 316, the method includes adjusting engine parameters in response tothe water injection. This may include but is not limited to decreasingan EGR flow rate only if an engine dilution demand is met, as describedabove. The method may exit.

FIG. 3 illustrated an exemplary method for utilizing a water injectionto either maintain a PF temperature or to decrease an ash load on the PFsurface nearest the space between a TWC and a PF. FIG. 4 will nowgraphically illustrate conditions during a PF regeneration and eventsleading to a water injection.

FIG. 4 illustrates plot 400 of various engine conditions affecting awater injection. It should be understood that the examples presented inFIG. 4 are illustrative in nature, and other outcomes are possible. Forexample, additional or alternative engine parameters may affect aregeneration occurrence. PF temperature has been omitted from FIG. 4.

FIG. 4 represents an example of an active regeneration, wherein acontroller may adjust engine parameters to initiate a PF regeneration(e.g., run engine lean, delay fuel injection, and/or retard spark).However, in alternative embodiments, the regeneration may be onlypassive, only active, or a combination thereof. If regeneration ispassive, the controller may not signal an adjustment to initiate thepassive PF regeneration.

The graphs in FIG. 4 represent various operating parameters andresultant engine controls for reducing an ash load on the PF surfacenearest the space between a TWC and a PF via a water injection into aspace between the TWC and the PF. The x-axis represents time and they-axis represents the respective engine condition being demonstrated. Onplot 400, graph 402 represents a soot load, graph 404 represents anexhaust gas temperature and line 405 represents a minimum thresholdexhaust gas temperature to begin a PF regeneration, graph 406 representsan exhaust pressure and line 408 represents a threshold exhaustpressure, graph 410 represents an ash load and line 411 represents athreshold ash load, and graph 412 represents a water injection. In theexample illustrated in FIG. 4, the threshold exhaust pressure 408represents the first threshold exhaust pressure and the second thresholdexhaust pressure, wherein the second threshold exhaust pressure is equalto the first threshold exhaust pressure.

Plot 400 will be described herein with reference to components andsystems depicted in FIG. 1, particularly, water reservoir 70,conduit/water injector 73, TWC 71, PF 72, exhaust pressure sensors 127and 128, and exhaust aftertreatment system 74. The parametersillustrated in plot 400 may be measured by a controller (e.g.,controller 12), according to computer-readable media stored thereon.

Prior to T1, the soot load increases, as seen with respect to graph 402.As the soot accumulates on the PF, the exhaust gas pressure increases,as shown on graph 406. The soot load may be increasing due to anincreased engine load and as a result, the exhaust gas temperatureincreases, as shown with respect to graph 404. The ash load remainsconstant and below the threshold ash load as no new soot is beingregenerated into ash, shown by graph 410. The water injection remainsdisabled, shown by graph 412.

At T1, the exhaust pressure increases to the threshold exhaust pressureand as a result, the controller may begin signaling adjustments to begina PF regeneration. The exhaust gas temperature is greater than theminimum threshold exhaust gas temperature to begin the PF regenerationdue to the adjustments signaled by the controller to begin aregeneration (e.g., increasing air intake, delaying fuel injection,and/or retarding spark). After T1 and prior to T2, the exhausttemperature continues to increase beyond the minimum threshold exhaustgas temperature. The minimum threshold regeneration exhaust gastemperature may be based on a threshold PF regeneration temperature(e.g., 600° C.). As described above, the PF regeneration efficacy may bedependent on the exhaust gas temperature, the soot load, and/or theduration of regeneration. Further, the duration of regeneration may bebased on the soot load, the exhaust gas temperature, and/or engineparameters (e.g., engine speed, engine load, engine temperature, etc.).As an example, the duration of regeneration and the exhaust gastemperature may be inversely related for a given soot load, wherein asthe exhaust temperature increases, the duration of regenerationdecreases.

The soot load remains high until the exhaust gas temperature increasesto a relatively high temperature. The high exhaust gas temperature(e.g., 900° C.) is a temperature greater than a low exhaust gastemperature (e.g., 550° C.). The exhaust pressure decreases to apressure below the threshold exhaust gas pressure. However, theregeneration duration may be based on a calculation comprising theregeneration temperature and the soot load, as described above, in orderto reduce the soot load to a relatively low amount, wherein theregeneration duration is independent of the exhaust pressure. Theexhaust gas temperature begins to decrease as the soot load decreases inorder to improve fuel economy (e.g. air/fuel ratio returns tostoichiometric, fuel injection timing is not delayed, and/or spark is nolonger retarded). Once the PF has reached the threshold PF regenerationtemperature, it may self-burn and no longer demand the exhaust gastemperature to be greater than the minimum threshold exhaust gastemperature to begin the PF regeneration. The ash load increases overthe length of the regeneration as the soot is converted to ash. The rateof ash load increase is not equivalent to the rate of soot loaddecrease, as the conversion of soot to ash is not 1:1 (e.g., burningsoot produces gas particles). The newly formed ash load is not above thethreshold ash load, and therefore the exhaust pressure remains below thethreshold exhaust pressure. As a result, the water injection remainsdisabled.

At T2, the PF regeneration ends and the soot load is low. The exhaustgas temperature decreases. The exhaust gas pressure remains below thethreshold exhaust gas pressure. The ash load remains below the thresholdash load, therefore, the water injection remains disabled. After T2 andprior to T3, the exhaust gas pressure increases as the soot load on thePF increases. The ash load remains constant due to the soot not beingregenerated into ash, as described above. The exhaust gas temperaturebegins to increase and the water injection remains disabled.

At T3, the exhaust pressure increases to a pressure greater than thethreshold exhaust gas pressure due to the increasing soot load. As aresult, the controller signals regeneration adjustments to increase theexhaust gas temperature, as described above. The ash load remainsconstant and below the threshold ash load due to the soot load not yetconverting into ash. At T3 and prior to T4, the exhaust gas temperatureincreases to a temperature substantially equal to the minimum thresholdexhaust gas temperature to begin the PF regeneration (e.g., 600° C.) andremains at that temperature. As a result, the PF regeneration durationis greater than the PF regeneration duration discussed above. This maybe due to a lower exhaust gas temperature (e.g., 600° C. compared to900° C.). The lower exhaust gas temperature may not heat the PF to adesired regeneration temperature as quickly as a higher exhaust gastemperature. As a result, the regeneration may take a longer period oftime. Further, the ash load rate of accumulation is decreased due to thelonger regeneration. The exhaust gas temperature begins to decreaseafter a duration of time, however, the regeneration continues until thesoot load is low, as described above.

At T4, the regeneration is complete and soot load is relatively low. Theexhaust temperature is decreasing to a relatively low temperature. Theexhaust pressure has deceased to a pressure below the threshold exhaustgas pressure. However, the reduction in the exhaust gas pressure is lessthan the reduction in the prior regeneration due to the ash loadincreasing over successive regenerations. However, the ash load remainsbelow the threshold ash load and the water injection is disabled. AfterT4 and prior to T5, the exhaust gas pressure increases due to anincreasing soot load on the PF. The exhaust temperature continues todecrease. The ash load remains constant and below the threshold ashload. Therefore, the water injection remains disabled.

At T5, the exhaust gas pressure reaches the threshold exhaust gaspressure. In response to the exhaust gas pressure being greater than orequal to the threshold exhaust gas pressure, the controller signalsadjustments to being the PF regeneration, as described above. Thesignaled adjustments cause the exhaust gas temperature to increase. Theexhaust gas temperature increases to a temperature greater than anominal exhaust temperature (e.g., 550° C.). The exhaust pressurecontinues to increase. The ash load does not increase due to the sootload not yet being converted into ash. The water injection remainsdisabled. After T5 and prior to T6, the exhaust gas temperatureincreases to a temperature greater than the minimum threshold exhaustgas temperature to begin the PF regeneration. In this example, theexhaust gas temperature may be less than the temperature of the firstregeneration (e.g., between T1 and T2) and greater than the temperatureof the second regeneration (e.g., between T3 and T4). Therefore, theregeneration duration between T5 and T6 is greater than the regenerationduration between T1 and T2 and less than the regeneration durationbetween T3 and T4. Once the PF reaches the threshold PF regenerationtemperature, the soot load begins to decrease. As the soot loaddecreases, the exhaust pressure decreases and the ash load increases.However, the ash load increases to an ash load greater than thethreshold ash load, therefore, the exhaust pressure is unable todecrease below the threshold exhaust gas pressure despite the PFregeneration. The regeneration continues until the soot reaches arelatively low load, as described above.

At T6, the regeneration is disabled and the soot load is relatively low.The exhaust gas temperature returns to the nominal exhaust gastemperature. The exhaust gas pressure between the TWC and the PF remainsgreater than the threshold exhaust gas pressure due to the ash loadbeing relatively high. In other words, the regeneration was initiatedresponsive to an exhaust gas pressure being greater than the thresholdexhaust gas pressure. However, the exhaust gas pressure being greaterthan the threshold exhaust gas pressure following a PF regeneration nolonger signals the PF regeneration, rather, it may signal an ash loadbeing greater than a threshold ash load. As a result, the waterinjection is initiated. After T6 and prior to T7, the water injectioncontinues at a constant rate over a predetermined period of time. Inalternative examples, the water injection rate may be adjustable basedon the estimated ash load on the PF, as described above. The exhaustpressure decreases below the threshold exhaust gas pressure. However,the water injection continues until the ash load decreases to arelatively low load. The exhaust gas temperature remains at a relativelylow temperature. The soot load increases at a low rate.

At T7, the water injection is deactivated due to the ash load reachingthe relatively low load.

In this way, an ash load accumulated onto a surface of a PF nearest aspace between the PF filter downstream of the TWC may be decreased.Further, the water injection may enhance the filtering abilities of thePF by increasing its adhesive surface area and providing hydrogen bondsfor regulated emission gases. The technical effect of performing thewater injection in the space between the TWC and the PF is to decreasethe ash load accumulated over PF regenerations to a level less than athreshold ash load. Further, the water injection may be responsive to aPF filter temperature above a threshold PF temperature. The waterinjection may decrease the PF filter temperature above the threshold PFtemperature in order to prevent PF degradation.

In an embodiment, method for an engine comprises injecting water from areservoir to between a particulate filter and a three-way catalyst, theparticulate filter located downstream of the three-way catalyst.Additionally or alternatively, the injecting is responsive to an exhaustpressure signal between the three-way catalyst and the particulatefilter being above a threshold pressure. The method may further includethe injecting being responsive to a particulate filter temperature beingabove a threshold temperature. Additionally or alternatively, theinjecting is responsive to an estimated ash load after a sootregeneration has been completed, wherein the estimated ash load is basedon an exhaust pressure after the soot regeneration, and furthercomprising adjusting a water injection amount based on the estimated ashload.

The method, additionally or alternatively, may include the three-waycatalyst comprises a porous substrate coated with one or more preciousmetals, the three-way catalyst configured to convert one or moreemissions in exhaust gas flowing through the three-way catalyst, andwherein the particulate filter comprises a mesh structure without aprecious metal coating, the particulate filter configured to trap sootin exhaust gas flowing through the gas particulate filter. Additionallyof alternatively, the soot regeneration is performed responsive to anexhaust gas pressure between the three-way catalyst and the particulatefilter being above a threshold exhaust gas pressure.

An embodiment of an engine comprises an engine with a plurality ofcylinders, an engine exhaust emission control device comprising aparticulate filter positioned downstream of a catalyst brick, an exhaustgas pathway coupling an engine exhaust manifold to the engine exhaustemission control device, an injector fluidically coupled to a waterreservoir via a conduit, the injector fluidically coupled between thecatalyst brick and the particulate filter, a pressure sensor coupledbetween the catalyst brick and the particulate filter, and a controllerhaving computer readable instructions stored on non-transitory memoryfor estimating an ash load in the particulate filter based on a pressuremeasured by the pressure sensor and injecting water via the injectorresponsive to the estimated ash load exceeding a threshold ash load. Thesystem, additionally or alternatively, may comprise an EGR pathwaycoupled to the exhaust pathway upstream of the emission control device,and wherein the instructions further comprise instructions for adjustingan EGR flow rate responsive to the injection of water.

The system may further include the three-way catalyst brick and theparticulate filter being housed in a common housing of the emissioncontrol device and separated via an air gap, and wherein the commonhousing includes a boss positioned between the three-way catalyst brickand the gas particulate filter to accommodate the injector, the injectorpositioned to inject water into the air gap, wherein the boss mayfurther accommodate the injector. Additionally or alternatively, thesystem may include the three-way catalyst brick and the particulatefilter being housed in separate housings and fluidically coupled via theexhaust pathway, and wherein the injector is coupled to the exhaustpathway between the three-way catalyst brick and the particulate filter.The system, additionally or alternatively, may include the estimated ashlevel being determined following completion of a regeneration of theparticulate filter.

Another method for an engine comprises combusting fuel in the engine viaspark ignition and directing exhaust gas from the engine to aparticulate filter, regenerating the particulate filter to removeparticulate matter stored on the particulate filter responsive toexhaust gas pressure upstream of the particulate filter exceeding afirst threshold pressure, and injecting water between the particulatefilter and a three-way catalyst upstream of the particulate filter toremove ash from the particulate filter responsive to the exhaust gaspressure upstream of the particulate filter exceeding a second thresholdpressure following completion of the regeneration. The method,additionally or alternatively, may include the exhaust pressure beingmeasured between the three-way catalyst and the particulate filter.

Additionally or alternatively, the method may include regenerating theparticulate filter, wherein the regenerating includes increasing exhaustgas temperature to at least a threshold temperature for a predeterminedduration, where the exhaust gas temperature and predetermined durationare determined based at least in part on a particulate matter load onthe particulate filter. The method, additionally or alternatively, mayinclude determining that the regeneration has reached completion whenthe exhaust gas temperature has been maintained at least at thethreshold temperature for the predetermined duration.

Additionally or alternatively, the method may include the exhaust gastemperature being increased as a result of an increase in engine load.The method may further include the first threshold pressure beinggreater than the second threshold pressure. The method, additionally oralternatively, may include injecting water to between the three-waycatalyst and the particulate filter when a particulate filtertemperature exceeds a threshold particulate filter temperature.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations and/or functions may graphically representcode to be programmed into non-transitory memory of the computerreadable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and non-obvious combinationsand sub-combinations of the various systems and configurations, andother features, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method, comprising: injecting water from a reservoir to between aparticulate filter and a three-way catalyst, the particulate filterlocated downstream of the three-way catalyst.
 2. The method of claim 1,wherein the injecting is responsive to an exhaust pressure signalbetween the three-way catalyst and the particulate filter being above athreshold pressure.
 3. The method of claim 1, wherein the injecting isresponsive to a particulate filter temperature being above a thresholdtemperature.
 4. The method of claim 1, wherein the three-way catalystcomprises a porous substrate coated with one or more precious metals,the three-way catalyst configured to convert one or more emissions inexhaust gas flowing through the three-way catalyst, and wherein theparticulate filter comprises a mesh structure with less precious metalcoating, the particulate filter configured to trap soot in exhaust gasflowing through the particulate filter.
 5. The method of claim 1,wherein the injecting is responsive to an estimated ash load after asoot regeneration has been completed.
 6. The method of claim 5, whereinthe estimated ash load is based on an exhaust pressure after the sootregeneration, and further comprising adjusting a water injection amountbased on the estimated ash load.
 7. The method of claim 5, wherein thesoot regeneration is performed responsive to an exhaust gas pressurebetween the three-way catalyst and the particulate filter being above athreshold exhaust gas pressure.
 8. A system, comprising: an engine witha plurality of cylinders; an engine exhaust emission control devicecomprising a particulate filter positioned downstream of a three-waycatalyst brick; an exhaust gas pathway coupling an engine exhaustmanifold to the engine exhaust emission control device; an injectorfluidically coupled to a water reservoir via a conduit, the injectorfluidically coupled between the three-way catalyst brick and theparticulate filter; a pressure sensor coupled between the three-waycatalyst brick and the particulate filter; and a controller havingcomputer readable instructions stored on non-transitory memory for:estimating an ash load in the particulate filter based on a pressuremeasured by the pressure sensor; and injecting water via the injectorresponsive to the estimated ash load exceeding a threshold ash load. 9.The system of claim 8, further comprising an EGR pathway coupled to theexhaust gas pathway upstream of the emission control device, and whereinthe instructions further comprise instructions for adjusting an EGR flowrate responsive to the injection of water.
 10. The system of claim 8,wherein the three-way catalyst brick and the particulate filter arehoused in a common housing of the emission control device and separatedvia an air gap, and wherein the common housing includes a bosspositioned between the three-way catalyst brick and the particulatefilter to accommodate the injector, the injector positioned to injectwater into the air gap.
 11. The system of claim 8, wherein the waterreservoir is coupled to one or more of a charge air cooler and an airconditioner, the water reservoir is replenished via condensate from oneor more of the charge air cooler and the air conditioner.
 12. The systemof claim 8, wherein the three-way catalyst brick and the particulatefilter are housed in separate housings and fluidically coupled via theexhaust pathway, and wherein the injector is coupled to the exhaustpathway between the three-way catalyst brick and the particulate filter.13. The system of claim 12, wherein the estimated ash load is determinedfollowing completion of a regeneration of the particulate filter.
 14. Amethod of an engine, comprising: combusting fuel in the engine via sparkignition and directing exhaust gas from the engine to a particulatefilter; responsive to an exhaust gas pressure upstream of theparticulate filter exceeding a first threshold pressure, regeneratingthe particulate filter to remove particulate matter stored on theparticulate filter; and responsive to the exhaust gas pressure upstreamof the particulate filter exceeding a second threshold pressurefollowing completion of the regeneration, injecting water between theparticulate filter and a three-way catalyst upstream of the particulatefilter to remove ash from the particulate filter.
 15. The method ofclaim 14, wherein the exhaust pressure is measured between the three-waycatalyst and the particulate filter.
 16. The method of claim 15, whereinregenerating the particulate filter includes increasing an exhaust gastemperature to at least a threshold temperature for a predeterminedduration, where the exhaust gas temperature and predetermined durationare determined based at least in part on a particulate matter load onthe particulate filter.
 17. The method of claim 16, further comprisingdetermining that the regeneration has reached completion when theexhaust gas temperature has been maintained at least at the thresholdtemperature for the predetermined duration.
 18. The method of claim 16,wherein the exhaust gas temperature is increased as a result of anincrease in engine load.
 19. The method of claim 14, wherein the firstthreshold pressure is greater than the second threshold pressure. 20.The method of claim 14, further comprising injecting water to betweenthe three-way catalyst and the particulate filter when a particulatefilter temperature exceeds a threshold particulate filter temperature.